Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$106.27	3.116%	$109.5814	$109.58	$109.60	$109.60
Purchase #2	$236.98	12.374%	$266.3039	$266.30	$266.30	$266.30
Purchase #3	$211.42	10.571%	$233.7692	$233.77	$233.75	$233.80
Purchase #4	$75.29	3.474%	$77.9056	$77.91	$77.90	$77.90
Purchase #5	$203.75	12.464%	$229.1454	$229.15	$229.15	$229.10
Purchase #6	$36.93	9.800%	$40.5491	$40.55	$40.55	$40.50
Purchase #7	$126.56	3.549%	$131.0516	$131.05	$131.05	$131.10
7 purchase totals =	$997.20		$1,088.3062	$1,088.31	$1,088.30	$1,088.30